We got eight vans out where I work, of various ages.
1. The Auto pilots are notoriously unreliable, a complaint I've heard from several operators. Though if looked after they do last longer, so only use in straight and level smooth air.
2. New vans come with the wing fences standard I think. This could explain your wallowing on landing, find with the fences she gets up faster. Also adds 350 to your max take off weight, not too bad for two little metal plates.
3. We had trouble with the ETM on one of our vans gave some real weird and fantastical readings.
4. As far as the controls being heavier, could just be a rigging and tension problem, find all of ours fly the same, though some are more stable than others.
5. Also in regards to the wallowing, find that the props are set diffrently sometimes between planes really making a diffrence when you put the power lever in idle on landing.
6. Never had any rust on our aircraft, then again they don't sit around long enough to collect any. Just some superficial salt air corrosion on the skin, but then we do operate along the coast and this only comes apparent after several years down here.
7. We never experienced any leaks on our vans, except when the lining of the pilot window wears out due to exposure to the sun. But easily fixed.
8. Suprised to hear about the carpets and cowling, never heard of anyone having problems with that, you sure they are brand new? Not refurbs or ex demo aircraft.